text: #ifndef _ASM_GENERIC_PGTABLE_H
  #define _ASM_GENERIC_PGTABLE_H
  
  #ifndef __HAVE_ARCH_PTEP_ESTABLISH
  /*
   * Establish a new mapping:
   *  - flush the old one
   *  - update the page tables
   *  - inform the TLB about the new one
   *
   * We hold the mm semaphore for reading, and the pte lock.
   *
   * Note: the old pte is known to not be writable, so we don't need to
   * worry about dirty bits etc getting lost.
   */
  #ifndef __HAVE_ARCH_SET_PTE_ATOMIC
  #define ptep_establish(__vma, __address, __ptep, __entry)		\
  do {				  					\
  	set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry);	\
  	flush_tlb_page(__vma, __address);				\
  } while (0)
  #else /* __HAVE_ARCH_SET_PTE_ATOMIC */
  #define ptep_establish(__vma, __address, __ptep, __entry)		\
  do {				  					\
  	set_pte_atomic(__ptep, __entry);				\
  	flush_tlb_page(__vma, __address);				\
  } while (0)
  #endif /* __HAVE_ARCH_SET_PTE_ATOMIC */
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
  /*
   * Largely same as above, but only sets the access flags (dirty,
   * accessed, and writable). Furthermore, we know it always gets set
   * to a "more permissive" setting, which allows most architectures
   * to optimize this.
   */
  #define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
  do {				  					  \
  	set_pte_at((__vma)->vm_mm, (__address), __ptep, __entry);	  \
  	flush_tlb_page(__vma, __address);				  \
  } while (0)
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
  #define ptep_test_and_clear_young(__vma, __address, __ptep)		\
  ({									\
  	pte_t __pte = *(__ptep);					\
  	int r = 1;							\
  	if (!pte_young(__pte))						\
  		r = 0;							\
  	else								\
  		set_pte_at((__vma)->vm_mm, (__address),			\
  			   (__ptep), pte_mkold(__pte));			\
  	r;								\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
  #define ptep_clear_flush_young(__vma, __address, __ptep)		\
  ({									\
  	int __young;							\
  	__young = ptep_test_and_clear_young(__vma, __address, __ptep);	\
  	if (__young)							\
  		flush_tlb_page(__vma, __address);			\
  	__young;							\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_DIRTY
  #define ptep_test_and_clear_dirty(__vma, __address, __ptep)		\
  ({									\
  	pte_t __pte = *__ptep;						\
  	int r = 1;							\
  	if (!pte_dirty(__pte))						\
  		r = 0;							\
  	else								\
  		set_pte_at((__vma)->vm_mm, (__address), (__ptep),	\
  			   pte_mkclean(__pte));				\
  	r;								\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_CLEAR_DIRTY_FLUSH
  #define ptep_clear_flush_dirty(__vma, __address, __ptep)		\
  ({									\
  	int __dirty;							\
  	__dirty = ptep_test_and_clear_dirty(__vma, __address, __ptep);	\
  	if (__dirty)							\
  		flush_tlb_page(__vma, __address);			\
  	__dirty;							\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
  #define ptep_get_and_clear(__mm, __address, __ptep)			\
  ({									\
  	pte_t __pte = *(__ptep);					\
  	pte_clear((__mm), (__address), (__ptep));			\
  	__pte;								\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL
  #define ptep_get_and_clear_full(__mm, __address, __ptep, __full)	\
  ({									\
  	pte_t __pte;							\
  	__pte = ptep_get_and_clear((__mm), (__address), (__ptep));	\
  	__pte;								\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTE_CLEAR_FULL
  #define pte_clear_full(__mm, __address, __ptep, __full)			\
  do {									\
  	pte_clear((__mm), (__address), (__ptep));			\
  } while (0)
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
  #define ptep_clear_flush(__vma, __address, __ptep)			\
  ({									\
  	pte_t __pte;							\
  	__pte = ptep_get_and_clear((__vma)->vm_mm, __address, __ptep);	\
  	flush_tlb_page(__vma, __address);				\
  	__pte;								\
  })
  #endif
  
  #ifndef __HAVE_ARCH_PTEP_SET_WRPROTECT
  struct mm_struct;
  static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long address, pte_t *ptep)
  {
  	pte_t old_pte = *ptep;
  	set_pte_at(mm, address, ptep, pte_wrprotect(old_pte));
  }
  #endif
  
  #ifndef __HAVE_ARCH_PTE_SAME
  #define pte_same(A,B)	(pte_val(A) == pte_val(B))
  #endif
  
  #ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_DIRTY
  #define page_test_and_clear_dirty(page) (0)
  #define pte_maybe_dirty(pte)		pte_dirty(pte)
  #else
  #define pte_maybe_dirty(pte)		(1)
  #endif
  
  #ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
  #define page_test_and_clear_young(page) (0)
  #endif
  
  #ifndef __HAVE_ARCH_PGD_OFFSET_GATE
  #define pgd_offset_gate(mm, addr)	pgd_offset(mm, addr)
  #endif
  
  #ifndef __HAVE_ARCH_LAZY_MMU_PROT_UPDATE
  #define lazy_mmu_prot_update(pte)	do { } while (0)
  #endif
  
  #ifndef __HAVE_ARCH_MULTIPLE_ZERO_PAGE
  #define move_pte(pte, prot, old_addr, new_addr)	(pte)
  #else
  #define move_pte(pte, prot, old_addr, new_addr)				\
  ({									\
   	pte_t newpte = (pte);						\
  	if (pte_present(pte) && pfn_valid(pte_pfn(pte)) &&		\
  			pte_page(pte) == ZERO_PAGE(old_addr))		\
  		newpte = mk_pte(ZERO_PAGE(new_addr), (prot));		\
  	newpte;								\
  })
  #endif
  
  /*
   * When walking page tables, get the address of the next boundary,
   * or the end address of the range if that comes earlier.  Although no
   * vma end wraps to 0, rounded up __boundary may wrap to 0 throughout.
   */
  
  #define pgd_addr_end(addr, end)						\
  ({	unsigned long __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;	\
  	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
  })
  
  #ifndef pud_addr_end
  #define pud_addr_end(addr, end)						\
  ({	unsigned long __boundary = ((addr) + PUD_SIZE) & PUD_MASK;	\
  	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
  })
  #endif
  
  #ifndef pmd_addr_end
  #define pmd_addr_end(addr, end)						\
  ({	unsigned long __boundary = ((addr) + PMD_SIZE) & PMD_MASK;	\
  	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
  })
  #endif
  
  #ifndef __ASSEMBLY__
  /*
   * When walking page tables, we usually want to skip any p?d_none entries;
   * and any p?d_bad entries - reporting the error before resetting to none.
   * Do the tests inline, but report and clear the bad entry in mm/memory.c.
   */
  void pgd_clear_bad(pgd_t *);
  void pud_clear_bad(pud_t *);
  void pmd_clear_bad(pmd_t *);
  
  static inline int pgd_none_or_clear_bad(pgd_t *pgd)
  {
  	if (pgd_none(*pgd))
  		return 1;
  	if (unlikely(pgd_bad(*pgd))) {
  		pgd_clear_bad(pgd);
  		return 1;
  	}
  	return 0;
  }
  
  static inline int pud_none_or_clear_bad(pud_t *pud)
  {
  	if (pud_none(*pud))
  		return 1;
  	if (unlikely(pud_bad(*pud))) {
  		pud_clear_bad(pud);
  		return 1;
  	}
  	return 0;
  }
  
  static inline int pmd_none_or_clear_bad(pmd_t *pmd)
  {
  	if (pmd_none(*pmd))
  		return 1;
  	if (unlikely(pmd_bad(*pmd))) {
  		pmd_clear_bad(pmd);
  		return 1;
  	}
  	return 0;
  }
  #endif /* !__ASSEMBLY__ */
  
  #endif /* _ASM_GENERIC_PGTABLE_H */
  